JP2004286685A - Gas concentration detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correctly detect an element current and enhance the detection precision of gas concentration. <P>SOLUTION: A gas concentration sensor 100 comprises a sensor element composed of a pump cell 110, a monitor cell 120 and a sensor cell 130, and these cells 110-130 are kept in an active state by heat produced by a heater 151. A sensor control unit 10 measures a weak element current flowing in the sensor element according to the concentration of a particular constituent and intermittently supplies power to the heater 151. The control unit 10 is electrically connected with the sensor 100 via wires H1-H4. The wires H2 and H3 through which the weak element current flows and the wire H4 through which a heater current flows are bundled. The wires H2 and H3 have a shielding layer provided on the outer side of a core wire on which the element current flows, with the layer being connected to the ground potential. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a gas concentration detection device that detects a gas concentration of a specific component in a gas to be detected.
[0002]
[Prior art]
As this type of gas concentration detecting device, there is a device which uses a limiting current type gas concentration sensor and detects, for example, NOx (nitrogen oxide) in exhaust gas discharged from a vehicle engine. The gas concentration sensor has a sensor element composed of, for example, a pump cell, a sensor cell, and a monitor cell. In the pump cell, oxygen in exhaust gas introduced into the chamber is discharged or pumped, and at the same time, oxygen concentration in the exhaust gas is detected. The sensor cell detects the NOx concentration (gas concentration of a specific component) from the gas after passing through the pump cell, and the monitor cell detects the residual oxygen concentration in the chamber after passing through the pump cell.
[0003]
In the above gas concentration sensor, the oxygen concentration and the NOx concentration are normally detected on the assumption that the sensor element is in a predetermined active state. Therefore, in general, a heater is provided near the sensor element, and the sensor element is heated by the heat generated by the heater to maintain the element active state. For example, the resistance value of a sensor element is detected, and the heater is intermittently energized so that the element resistance value becomes a target value corresponding to the activation temperature (for example, see Patent Document 1).
[0004]
More specifically, in a so-called NOx sensor as a gas concentration sensor, NOx in exhaust gas is decomposed at a NOx active electrode of a sensor cell, and oxygen ions generated at that time flow in the sensor cell. At this time, the NOx concentration is detected by measuring the current flowing in the sensor cell. The sensor cell current is a weak current on the order of nA (nanoampere), and the weak current is measured through a high-resistance (for example, 1.5 MΩ) current detection resistor in the sensor control circuit. On the other hand, the heater is energized intermittently by the heater drive circuit. At this time, the heater current on the order of A (ampere) is ON / OFF controlled.
[0005]
Generally, a sensor control circuit and a heater drive circuit are mounted on the same circuit board, and the circuit board is housed in a metal case or the like to form a sensor control unit. The sensor control unit and the gas concentration sensor are electrically connected via a wiring unit, and between them, an element current signal such as a sensor cell current and a heater current signal flow through the wiring unit. The electric wiring constituting the wiring unit is covered with a covering material made of a resin material or the like in consideration of heat resistance. As the coating material, for example, a resin material such as a glass braided silicon coating material, silicon knitted EPDM rubber, nylon, or polyamide is used.
[0006]
[Patent Document 1]
JP-A-2000-171435
[0007]
[Problems to be solved by the invention]
The wiring unit that electrically connects the sensor control unit and the gas concentration sensor includes an electric wiring through which a weak element current of the order of nA flows and an electric wiring through which a heater current of the order A flows, and these are usually bundled. It is designed to be managed around. In this case, when the element current and the heater current are simply compared, the current level is 10 ⁹ Therefore, noise (induction noise or capacitive coupling noise) generated when the heater is turned on / off may be superimposed on the electric wiring for the element current, and the necessary detection accuracy of the NOx concentration may not be secured. Was. Such a problem has also been confirmed in a radio wave test (EMC test). In recent years, various types of electric devices mounted on vehicles have been increasing more and more, and there is also a background that noise sources affecting element current signals are increasing.
[0008]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas concentration detection device capable of correctly detecting an element current and improving the detection accuracy of a gas concentration. .
[0009]
[Means for Solving the Problems]
The gas concentration sensor includes a sensor element having a solid electrolyte and detecting a gas concentration of a specific component in a gas to be detected, and a heater for heating the sensor element to a predetermined active state. The detection device is applied to this gas concentration sensor. The gas concentration sensor and the sensor control unit are electrically connected through a wiring unit. In the sensor control unit, a weak element current flowing through the sensor element corresponding to the specific component concentration is measured, and the heater is turned on and off. Is to be energized.
[0010]
According to the first aspect of the present invention, the wiring unit is formed by bundling an element current line for flowing an element current and a heater line for supplying power to a heater, wherein the element current line has a core wire through which the element current flows. Also, a shield layer having a ground potential is provided on the outside. Since the element current flowing on the element current line side is weak, it is affected by induction noise and capacitive coupling noise from the heater line. However, as described above, a shield layer is provided outside the element current line core wire (that is, around the core wire). With the provision, the influence of these noises can be eliminated. In addition, since the noise resistance is improved, it is possible to appropriately cope with an increase in noise sources due to an increase in various types of electric devices mounted on the vehicle. As a result, the element current can be correctly detected, and the detection accuracy of the gas concentration can be improved.
[0011]
As described in claim 2, in the element current line, the periphery of the core wire may be covered with a covering layer, and the outside of the covering layer may be covered with the shield layer. In such a configuration in which the coating layer is interposed between the core wire and the shield layer, there is a possibility that the device current leaks through the coating layer due to the potential difference between the core wire and the shield layer. Therefore, in order to suppress the leakage of the device current, as a characteristic of the coating layer, the coating layer has a volume resistivity of 1.0 × 10 3 as described in claim 3. ¹² (Ω · cm) or more.
[0012]
In order to satisfy the above characteristics of the coating layer, it is preferable to use Teflon (registered trademark) as the coating layer, as described in claim 4. The volume resistivity required for the coating layer varies depending on conditions such as the required accuracy of the device current and the length of the wiring, but the volume resistivity of Teflon (registered trademark) is 1.0 × 10 ¹⁸ (Ω · cm) or more, and satisfies the condition defined in claim 3 with a margin. Therefore, by using Teflon (registered trademark) as the coating layer, the leakage of the device current can be reliably suppressed.
[0013]
In the invention described in claim 5, the element current line has a plurality of core wires, and the plurality of core wires are collectively covered with the shield layer. In this case, a plurality of core wires can be aggregated, and the unity as element current lines can be improved. The core wires covered by the shield layer collectively cause a weak current to flow through them, and there is no mutual influence such as noise.
[0014]
Claims 6 and 7 can be applied to the configuration of the element current line. That is, in the invention according to claim 6, the element current line has a core wire covered with a coating layer, a shield layer is provided outside the core wire, and a protection layer is further provided outside the core layer. In the invention according to claim 7, the element current line has a plurality of core wires each covered with a coating layer, a shield layer is provided outside the plurality of core wires, and a protection layer is further provided outside the core layer. It shall be assumed.
[0015]
In the invention described in claim 8, ground processing for connecting the shield layer of the element current line to the ground potential and ground processing for connecting the heater to the ground potential are separately performed. As a result, even if the ground potential (reference potential) on the heater side fluctuates, it is possible to avoid such a disadvantage that the ground potential on the shield layer side is adversely affected.
[0016]
According to the ninth aspect of the present invention, the wiring unit is connected to the sensor control unit via a connector member, and the outer periphery of the connector member is shielded. Thereby, the noise resistance of the connector member is improved, and a more desirable configuration can be realized in order to improve the detection accuracy of the gas concentration.
[0017]
In the invention according to claim 10, an element current connector for connecting the element current line to the sensor control unit and a heater connector for connecting the heater line to the sensor control unit are separately provided. Provided. As a result, the noise resistance of the element current connector is improved, and a more desirable configuration can be realized in order to improve the detection accuracy of the gas concentration. In addition, it is possible to further improve the noise resistance by providing a shield on the outer periphery of the element current connector.
[0018]
According to the present invention, the control circuit portion included in the sensor control unit is housed in a closed space of a case made of a conductive material and having a ground potential, and a feedthrough capacitor is provided on a wall portion of the case. And a connection circuit section electrically connected to the wiring unit was disposed outside the closed space, and the connection circuit section and the control circuit section were electrically connected through a feedthrough capacitor. According to this configuration, external radio noise superimposed on the wiring unit is absorbed by the feedthrough capacitor. Further, since the control circuit section of the sensor control unit is arranged in a closed space separated from the connection circuit section (wiring unit), the influence of external noise and the like on the control circuit section can be reliably eliminated. In this case, the sensor control unit handles a weak element current, and the specific component concentration is detected by the element current. At this time, however, adverse effects due to radio noise and the like can be suppressed. As a result, the element current can be correctly detected, and the detection accuracy of the gas concentration can be improved.
[0019]
According to the twelfth and twelfth aspects of the present invention, a case made of a conductive material and having a ground potential is divided into two rooms by a partition plate made of the same conductive material and having a ground potential, and a feedthrough capacitor is provided in the partition plate. And a control circuit unit included in the sensor control unit and a connection circuit unit electrically connected to the wiring unit are accommodated in the two rooms, respectively, and these circuit units are electrically connected through a feedthrough capacitor. According to this configuration, external radio noise superimposed on the wiring unit is absorbed by the feedthrough capacitor. Further, since the control circuit section of the sensor control unit is provided in a separate room separated from the connection circuit section, the influence of external noise and the like on the control circuit section can be reliably eliminated. In this case, the sensor control unit handles a weak element current, and the specific component concentration is detected by the element current. At this time, however, adverse effects due to radio noise and the like can be suppressed. As a result, the element current can be correctly detected, and the detection accuracy of the gas concentration can be improved.
[0020]
According to the twelfth and fourteenth aspects of the present invention, as described in the fifteenth aspect, the control circuit section and the connection circuit section are provided on the same circuit board, and the control circuit section and the connection circuit section are provided on the circuit board so as to stand between the two circuit sections. The partition plate may be installed at the same time. In this case, the surface on which the wiring units are connected on the circuit board is preferably the same as the surface on which the partition plate is erected.
[0021]
The capacitance of the feedthrough capacitor is preferably 1000 pF or more.
[0022]
In addition, for example, a NOx sensor that detects NOx in automobile exhaust gas detects a NOx concentration from a pump cell that regulates the flow of oxygen in and out of the chamber, and NOx concentration from the amount of oxygen ions that travels at the time of decomposing NOx from gas that has passed through the pump cell. And the current flowing through the sensor cell is a weak current on the order of nA. The present invention can be suitably applied to such a NOx sensor. In short, as described in claim 17, the sensor element includes a first cell for discharging or pumping oxygen in the gas to be detected introduced into the chamber, and a gas after passing through the first cell for taking in the gas. A second cell for decomposing the specific component and detecting the gas concentration of the specific component from the amount of oxygen ions moving at that time, wherein the sensor control unit measures at least a weak current flowing through the second cell. And good.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to the drawings. The gas concentration detection device according to the present embodiment is applied to, for example, an automobile engine, and uses a limiting current type gas concentration sensor to determine the oxygen concentration in the exhaust gas to be detected or the gas concentration of a specific component. Is detected.
[0024]
First, the configuration of the gas concentration sensor will be described with reference to FIGS. The gas concentration sensor has a three-cell structure including a pump cell as a “first cell”, a sensor cell as a “second cell”, and a monitor cell as a “third cell”, and measures the oxygen concentration and NOx concentration in exhaust gas. It is embodied as a so-called composite gas sensor that can be detected at the same time (however, it can be embodied as a NOx sensor). In the present embodiment, a sensor element is constituted by the three cells. Note that the monitor cell may be referred to as a second pump cell because it has a function of discharging oxygen in gas, similarly to the pump cell. FIG. 6A is a cross-sectional view showing a tip structure of the sensor element, and FIG. 6B is a cross-sectional view taken along line AA of FIG. 6A. FIG. 7 is an overall view showing the appearance of the gas concentration sensor.
[0025]
As shown in FIG. 7, the gas concentration sensor 100 has a front cover 101, a housing 102, and a base cover 103, and has a substantially columnar shape as a whole. A gas chamber for introducing the gas to be detected, an air chamber for introducing the atmosphere, and the like are appropriately provided inside the sensor, and a long sensor element 105 is provided.
[0026]
As shown in FIG. 6, in the gas concentration sensor 100 (sensor element 105), the solid electrolytes 141 and 142 made of an oxygen ion conductive material are formed in a sheet shape, and the solid electrolytes 141 and 142 are formed through a spacer 143 made of an insulating material such as alumina. They are vertically stacked at predetermined intervals. Among them, a pinhole 141a is formed in the solid electrolyte 141 on the upper side of the figure, and exhaust gas around the sensor is introduced into the first chamber 144 via the pinhole 141a. The first chamber 144 communicates with the second chamber 146 via the throttle 145. Reference numeral 147 is a porous diffusion layer.
[0027]
A pump cell 110 is provided in the lower solid electrolyte 142 so as to face the first chamber 144, and the pump cell 110 discharges or pumps oxygen in exhaust gas introduced into the first chamber 144. It works and detects the oxygen concentration in the exhaust gas when discharging or pumping oxygen. Here, the pump cell 110 has a pair of upper and lower electrodes 111 and 112 with the solid electrolyte 142 interposed therebetween. Among them, the electrode 111 on the side of the first chamber 144 is a NOx inert electrode (an electrode that hardly decomposes NOx gas). . The pump cell 110 decomposes oxygen existing in the first chamber 144 and discharges the oxygen from the electrode 112 to the atmosphere passage 150 side.
[0028]
Further, a monitor cell 120 and a sensor cell 130 are provided on the solid electrolyte 141 on the upper side of the figure so as to face the second chamber 146. The monitor cell 120 generates an electromotive force according to the residual oxygen concentration in the second chamber 146, or generates a current output according to the application of a voltage. The sensor cell 130 detects the NOx concentration from the gas after passing through the pump cell 110.
[0029]
In particular, in the present embodiment, as shown in FIG. 6B, the monitor cell 120 and the sensor cell 130 are arranged in parallel so as to be at the same position with respect to the flow direction of the exhaust gas, and the respective cells 120, 130 The electrode on the side of the atmosphere passage 148 is the common electrode 122. That is, the monitor cell 120 is composed of the solid electrolyte 141 and the electrode 121 and the common electrode 122 disposed opposite each other with the solid electrolyte 141 interposed therebetween, and the sensor cell 130 is similarly configured with the solid electrolyte 141 and the electrode 131 disposed opposite thereto with the electrode 131 interposed therebetween. And an electrode 122. The electrode 121 (electrode on the second chamber 146 side) of the monitor cell 120 is made of a noble metal such as Au-Pt which is inert to NOx gas, whereas the electrode 131 (electrode on the second chamber 146 side) of the sensor cell 130 is It is made of a noble metal such as platinum Pt or rhodium Rh which is active in NOx gas.
[0030]
An insulating layer 149 made of alumina or the like is provided on the lower surface of the solid electrolyte 142 in the figure, and the insulating layer 149 forms an air passage 150. Further, a heater (heating element) 151 for heating the entire sensor is embedded in the insulating layer 149. The heater 151 generates thermal energy by supplying power from a battery power source or the like to activate the entire sensor element including the pump cell 110, the monitor cell 120, and the sensor cell 130.
[0031]
In the gas concentration sensor 100 having the above configuration, the exhaust gas is introduced into the first chamber 144 through the porous diffusion layer 147 and the pinhole 141a. When this exhaust gas passes near the pump cell 110, a decomposition reaction occurs by applying a voltage Vp between the pump cell electrodes 111 and 112, and oxygen is passed through the pump cell 110 according to the oxygen concentration in the first chamber 144. Get in and out. At this time, since the electrode 111 on the first chamber 144 side is a NOx inactive electrode, NOx in the exhaust gas is not decomposed in the pump cell 110, and only oxygen is decomposed and discharged to the atmosphere passage 150. Then, the concentration of oxygen contained in the exhaust gas is detected based on the current flowing through the pump cell 110 (pump cell current Ip).
[0032]
The exhaust gas that has passed near the pump cell 110 flows into the second chamber 146, and the monitor cell 120 generates an output according to the residual oxygen concentration in the gas. The output of the monitor cell 120 is detected as a monitor cell current Im by applying a predetermined voltage Vm between the monitor cell electrodes 121 and 122. In addition, when a predetermined voltage Vs is applied between the sensor cell electrodes 131 and 122, NOx in the gas is reduced and decomposed, and oxygen generated at that time is discharged to the atmosphere passage 148. At this time, the concentration of NOx contained in the exhaust gas is detected based on the current flowing through the sensor cell 130 (sensor cell current Is).
[0033]
Incidentally, in the pump cell 110, the applied voltage Vp is variably controlled according to the oxygen concentration in the exhaust gas (that is, the pump cell current Ip) in each case. For example, based on the limit current characteristic of the pump cell 110, Using the created applied voltage map, the applied voltage Vp is controlled according to the pump cell current Ip in each case. Thereby, the applied voltage control is performed such that the applied voltage shifts to the higher voltage side as the oxygen concentration in the exhaust gas increases.
[0034]
FIG. 1 is a block diagram showing a system configuration of the gas concentration detection device. In FIG. 1, a sensor control unit 10 has a sensor control unit 11, a heater control unit 12, and an input / output unit (I / O port) 13, and the sensor control unit 11 is connected via electric wires H1, H2, and H3. The pump cell 110, the monitor cell 120, and the sensor cell 130 are electrically connected to each other. As is well known, the sensor control unit 11 applies a function of applying a predetermined applied voltage to each of the cells 110 to 130 of the gas concentration sensor 100 and a current signal (element current) flowing through each of the cells 110 to 130 through a current detection resistor. It has a function to measure.
[0035]
In this case, a current signal on the order of mA (milliamperes) flowing through the pump cell 110 flows through the electric wiring H1 to the sensor control unit 11, and is measured by a current detection resistor in the control unit 11. Then, the oxygen concentration (A / F) in the exhaust gas is detected based on the measured pump cell current signal. Further, a current signal on the order of nA (nano-amperes) flowing through the monitor cell 120 and the sensor cell 130 flows to the sensor control unit 11 via the electric wirings H2 and H3, and each of them is measured by a current detection resistor in the control unit 11. . Then, the residual oxygen concentration in the second chamber 146 is detected based on the monitor cell current signal, and the NOx concentration is detected based on the sensor cell current signal. At this time, the detected values of the oxygen concentration and the NOx concentration are output to the external engine ECU 20 and the like through the input / output unit 13 and the electric wiring H5.
[0036]
Further, the heater control unit 12 is electrically connected to the heater 151 via the electric wiring H4, and the heater 151 is intermittently energized by the heater control unit 12. That is, the heater control unit 12 includes a switching element (for example, a MOSFET), a driver for driving, and the like, and the power supplied to the heater 151 is PWM-controlled by a Duty signal output from an arithmetic unit such as a CPU. .
[0037]
The electric wirings H1 to H5 are generally bundled by a binding band such as Tie Wrap (registered trademark) in consideration of handling and the like, and constitute a wiring unit together with connector portions provided at both ends of the wiring ( Illustration is omitted). The electric wires H2 and H3 connected to the monitor cell 120 and the sensor cell 130, in particular, pass a weak element current of nA level, which corresponds to the "element current line", and the electric wires H4 connected to the heater 151. Is for passing an A-level current, which corresponds to a “heater wire”.
[0038]
In the sensor control unit 10, various electric components, microcomputers, and the like for constituting the sensor control unit 11 and the heater control unit 12 are mounted on the same sensor control circuit board, and the circuit board has a thin rectangular box shape. Housed in a case. In this case, the sensor control unit 11 includes a circuit configuration for detecting a weak current of the nA level, and it is necessary to minimize external noise. Hereinafter, a characteristic configuration of the sensor control unit 10 including noise measures will be described.
[0039]
FIG. 2 is a diagram showing a specific configuration of the sensor control unit 10, and FIG. 2A is a perspective view showing a configuration of the sensor control unit 10 in a state where a cover 37 is removed from a case main body 31 of a case 30. (B) is an XX sectional view of the same unit 10.
[0040]
The case body 31 is formed in a box shape with a bottom by a conductive material such as a metal such as aluminum or a conductive plastic, and the inside of the case is divided into two rooms by a partition plate 32 also made of a conductive material. In this case, the sensor control circuit board 33 is housed in one room, and the wiring connection board 34 is housed in the other room. The case body 31 and the partition plate 32 that comes into contact with the case body 31 are both at the ground potential. The sensor control circuit board 33 corresponds to a “control circuit section”, and the wiring connection board 34 corresponds to a “connection circuit section”. In the following description, a room accommodating the sensor control circuit board 33 is referred to as a first room A, and a room accommodating the wiring connection board 34 is referred to as a second room B for convenience.
[0041]
A plurality of feedthrough capacitors 35 are attached to the partition plate 32 in a horizontal row, and the partition plate 32 is brought into contact with the case main body 31 to be electrically connected, so that the internal terminals of the feedthrough capacitor 35 are connected to the partition plate 32 and the case main body 31. Is connected to the ground. Lead wires 35a and 35b extending from both ends of the feedthrough capacitor 35 are connected to a sensor control circuit board 33 and a wiring connection board 34, respectively, and the boards 33 and 34 are electrically connected through the feedthrough capacitor 35. It is preferable that the feedthrough capacitor 35 has a capacitance characteristic of 1000 pF or more. In this configuration, the partition plate 32 not only serves to divide the inside of the case 30 into two rooms, but also serves to hold the plurality of feedthrough capacitors 35 and connect the internal terminals thereof to ground.
[0042]
FIG. 2 illustrates five feedthrough capacitors 35, which are simply shown, and are actually the same as the number of connection terminals provided on the sensor control circuit board 33, that is, As many through capacitors 35 as the number of core wires (wires) included in the wirings H1 to H5 are provided.
[0043]
Further, a wiring cutout 36 cut into a rectangular shape is formed on one side surface of the case main body 31, and the electric wirings H1 to H5 are taken into the case 30 through the wiring cutout 36, The electrical connection to the wiring connection board 34 is made. Then, as described above, the lid 37 is attached in a state where the partition plate 32 and the circuit boards 33 and 34 are arranged in the case main body 31. As a result, the first chamber A that houses the sensor control circuit board 33 is in a substantially sealed state.
[0044]
According to the configuration of the sensor control unit 10, the first chamber A for housing the sensor control circuit board 33 is provided substantially separated from the second chamber B for housing the wiring connection board 34, and the potential of the case 30 is further reduced. Since the first chamber A is at the ground potential, the influence of external radio noise entering the second chamber B on the first chamber A side can be eliminated. In addition, the radio wave noise superimposed on the electric wirings H1 to H5 can be absorbed by the through capacitor 35. As described above, the stable operation of the sensor control circuit board 33 can be maintained, and the reliability is improved.
[0045]
On the other hand, among the electric wirings H1 to H4 that electrically connect the gas concentration sensor 100 and the sensor control unit 10 as described above, the electric wirings H2 and H3 that flow a weak element current of the nA level, in particular, run parallel to this. However, there is a concern that the detection accuracy of the NOx concentration is reduced as a result of being affected by induction noise and capacitive coupling noise from the electric wiring H4 through which the heater current of the A level flows. Therefore, as a countermeasure against noise of the electric wirings H2 and H3, a configuration in which a shield is added to the electric wirings H2 and H3 is adopted. It should be noted that no shielding is added to the electric wirings H1 and H4 through which a relatively large current flows, and a conventional resin coating configuration is adopted.
[0046]
FIG. 3 is a perspective view showing a wiring structure for embodying the electric wirings H2 and H3. FIG. 3 shows a multi-core structure in which a plurality of (two in the figure) core wires are collectively covered with a shield layer. ing.
[0047]
In FIG. 3, the core wires 41 are individually covered with a covering layer 42 made of an insulating material, and they are collectively covered with a shield layer 43 made of a braided shield. Further, the outer periphery of the shield layer 43 is covered with a vinyl sheath 44. The shield layer 43 is made of a highly conductive material such as a tin-plated soft copper wire or a stainless (SUS304) -based material, and its braid density is desirably 90% or more. However, instead of the braided shield, it is also possible to use a horizontal winding shield, a conductor tape or the like, and any material and structure that can substantially obtain the shielding effect may be used. Reference numeral 45 in the figure denotes a drain wire. For example, when the drain wire 45 is connected to the case 30 of the sensor control unit 10, the potential of the shield layer 43 is reduced to the ground potential.
[0048]
As a configuration of the electric wires H2 and H3, the core wires 41 may be individually covered one by one with a shield layer 43, and FIG. 4 shows the structure.
[0049]
FIG. 5 is a sectional view showing various forms of the shield coating. In FIG. 5A, a core wire 41 is covered with a coating layer 42, a shield layer 43 is provided outside the core wire 41, and a vinyl sheath 44 as a protective layer is further provided outside (the outermost periphery). In FIG. 5B, a plurality of core wires 41 are each covered with a coating layer 42, a shield layer 43 is provided on the outside, and a vinyl sheath 44 is provided on the outside (outermost circumference). A drain wire 45 is provided inside the shield layer 43 so as to be in contact with the shield layer 43. In FIG. 5C, a plurality of core wires 41 are each covered with a coating layer 42, and a shield layer 43 is provided on the outside thereof. Then, the shield layer 43 is directly dropped to the ground potential. Each of the above configurations has a configuration as a coaxial cable.
[0050]
In the above wiring structure, in the electric wires H2 and H3, the shield layer 43 covering the core wire 41 is provided around the core wire 41 and the shield layer 43 is set to the ground potential, so that the induction noise and the capacitive coupling from the electric wire H4 for the heater are provided. The effects of external noise such as noise and other radio noise can be eliminated. Therefore, the originally intended nA-level element current can be accurately detected.
[0051]
In the electric wires H2 and H3 configured as described above, a voltage of about 1 V is applied to the core wire 41, while the potential of the shield layer 43 is reduced to the ground potential. There is a concern that leakage current (leak current) may occur. Therefore, in order to eliminate the influence of the leakage current through the coating layer 42, the volume resistivity ρ, which is a characteristic of the coating layer 42, is set to 1.0 × 10 ¹² (Ω · cm) or more.
[0052]
In short, as shown in FIG. 8, when the average cross-sectional area of a material is S (cm 2), the measured distance of electric resistance is L (cm), and the electric resistance value is R (Ω), the volume resistivity ρ ( Ωcm)
ρ = (S / L) × R (1)
Is represented by the relationship This relationship will be re-examined in the covering layer of the electric wiring. FIG. 9 shows an electric wiring having a single-core structure. In FIG. 9, the same component numbers as those in FIGS. FIG. 9A is a perspective view showing an appearance of the electric wiring, and FIG. 9B is a front view showing a layer structure of the electric wiring.
[0053]
In FIG. 9, Rs is the core wire radius, Ww is the length of the coating layer 42, and the distance between the core wire 41 and the shield layer 43 (that is, the thickness of the coating layer 42) corresponds to the measurement distance L. In this case, the average cross-sectional area S can be represented by “S = π (2Rs + L) × Ww”. When this is applied to the above equation (1), the following equation is obtained.
[0054]
ρ = R × {π (2Rs + L) × Ww} / L (2)
Here, assuming that the element current flowing through the monitor cell 120 and the sensor cell 130 is about 500 nA (0.5 μA) and the allowable leakage current is 0.2% (1 nA) of the element current, the coating layer 42 is required. The resistance value R becomes 1 GΩ or more (R = 1 (V) / 1 (nA) ≧ 1 × 10 ⁹ Ω = 1 GΩ). Further, if Rs = 0.05 cm, L = 0.05 cm, and Ww = 100 cm according to the specifications of general electric wire materials, then, from the above equation (2), the volume resistivity ρ ≧ 0.94 × 10 ¹² (Ω · cm). Therefore, ρ ≧ 1.0 × 10 ¹² (Ω · cm), the required accuracy of the element current is satisfied.
[0055]
When Teflon (registered trademark) is used as the coating layer 42, the volume resistivity ρ ≧ 10 ¹⁸ (Ω · cm), which satisfies the above requirements with a margin. However, besides Teflon (registered trademark), volume resistivity ρ ≧ 10 ¹² (Ω · cm), a coating layer made of another material may be employed. For example, when an AV wire generally used as an automobile wire is used, the volume resistivity ρ on the specification is 10 ¹⁰ -10 ^Fifteen (Ω · cm) and volume resistivity ρ ≧ 10 ¹² (Ω · cm) can be used as the coating layer 42 by managing the content to satisfy (Ω · cm). When Teflon (registered trademark) is used, there is also an advantage that the troublesome management is released.
[0056]
In the above calculation example, it is assumed that the covering layer length Ww is 100 cm and the core voltage is 1 V. However, the longer the covering layer length Ww, the smaller the resistance value R, and the higher the core voltage, the larger the leakage current. Therefore, the volume resistivity ρ ≧ 10 ¹⁸ It is considered that the use of a Teflon (registered trademark) wire of (Ω · cm) works more advantageously against leakage current (leakage current).
[0057]
Although not shown, in the present embodiment, the ground processing for connecting the shield layer 43 to the ground potential and the ground processing for connecting the heater 151 to the ground potential in the electric wirings H2 and H3 for passing a weak element current are described. It is configured to be applied separately. Specifically, the shield layers 43 of the electric wires H2 and H3 are connected to the ground of the sensor control unit 10, and the negative terminal of the heater 151 is connected to the ground of the engine or the engine ECU 20. As a result, even if the ground potential (reference potential) on the heater 151 side fluctuates, it is possible to avoid such a disadvantage that the ground potential on the shield layer 43 side is adversely affected.
[0058]
The connector unit constituting the wiring unit may be configured to shield the outer periphery of the connector unit. For example, as shown in FIG. 10, a casing 61 as a shielding material is put around the connector portion 60. In this case, the connector portion 60 is made of a resin molded product, and the casing 61 is made of a material having high conductivity such as metal. Casing 61 is at ground potential. Instead of the casing 61, a configuration in which a conductor tape or the like is wound around the outer periphery of the connector section 60 may be employed. Thereby, the noise resistance of the connector section 60 is improved, and a more desirable configuration can be realized in order to improve the detection accuracy of the gas concentration (NOx concentration in the present embodiment).
[0059]
Also, an element current connector for connecting the electric wires H2 and H3 for passing a weak element current to the sensor control unit 10, and a heater connector for connecting the electric wire H4 for the heater to the sensor control unit 10 are provided. May be separately provided. As a result, the noise resistance of the element current connector is improved, and a more desirable configuration can be realized in order to improve the detection accuracy of the gas concentration. In addition, it is also possible to provide a shield (for example, the casing 61 in FIG. 10) on the outer periphery of the element current connector to further improve noise resistance.
[0060]
According to the present embodiment described in detail above, the following excellent effects can be obtained.
[0061]
By providing the shield layer 43 around the core wire 41 in the electric wires H2 and H3 for the element current, the influence of the induction noise and the capacitive coupling noise received from the electric wire H4 for the heater can be eliminated. In addition, since the noise resistance is improved, it is possible to appropriately cope with an increase in noise sources due to an increase in various types of electric devices mounted on the vehicle. As a result, the element current can be correctly detected, and the detection accuracy of the gas concentration (NOx concentration in the present embodiment) can be improved. As a countermeasure against noise, it is conceivable to arrange and manage the electric wirings H2 and H3 through which a weak current flows and the electric wiring H4 through which a heater current flows, but according to the present embodiment, such management is troublesome. You will be released from it.
[0062]
The coating layer 42 has a volume resistivity of 1.0 × 10 ¹² (Ω · cm) or more, for example, Teflon (registered trademark) is used, so that leakage of element current through the coating layer 42 can be reliably suppressed. Therefore, the reliability of the element current detection result is further improved.
[0063]
Further, the external radio noise superimposed on the electric wirings H1 to H5 is absorbed by the feedthrough capacitor 35 immediately before reaching the sensor control circuit board 33, and the sensor control circuit board 33 is connected to the wiring connection board 34 (the electric wirings H1 to H5). 2), the sensor control circuit board 33 can be reliably prevented from being affected by external noise and the like. Therefore, even with such a configuration, the element current can be correctly detected, and the detection accuracy of the gas concentration can be improved.
[0064]
Since the partition plate 32 has both a role of holding the feedthrough capacitor 35 and a role of dividing the inside of the case 30 into two rooms, there is no need to additionally provide a wall dedicated to the partition, and the above-described effect is obtained with a simple structure. Can be
[0065]
The present invention is not limited to the description in the above embodiment, and may be implemented, for example, as follows.
[0066]
The configuration of the sensor control unit 10 is as shown in FIG. 11 is different from the configuration of FIG. 2 in that one circuit board 51 is arranged over substantially the entire case body 31 and a partition plate 52 is erected on the circuit board 51. The partition plate 52 not only has a function of holding the feedthrough capacitor 35 as in FIG. 2 but also has a function of dividing the inside of the case 30 (in particular, the space above the circuit board 51) into two rooms. In this case, the surface for connecting the electric wirings H1 to H5 on the circuit board 51 is the same as the surface on which the partition plate 52 is erected. In the circuit board 51, the left side of the drawing from the partition plate 52 is a control circuit section, and the right side of the drawing is a connection circuit section. Also in this configuration, since the control circuit section and the connection circuit section are separated by the partition plate 52, the influence of external noise or the like on the control circuit section can be reliably eliminated.
[0067]
In the above embodiment, the control circuit section (sensor control circuit board) and the connection circuit section (wiring connection board) are both housed in the case 30, but the connection circuit section is separately provided outside the case. Is also good. In short, the control circuit section (sensor control circuit board) is housed in the closed space of the case, the feedthrough capacitor is arranged on the wall of the case, and the connection circuit section (wiring connection board) is arranged outside the closed space. Then, any configuration may be used as long as the connection circuit section and the control circuit section are electrically connected through a feedthrough capacitor. According to this configuration, the influence of external noise or the like on the control circuit section can be reliably eliminated, and the element current can be correctly detected.
[0068]
In the above embodiment, since the current level of the pump cell current is higher than the monitor cell current and the sensor cell current, the electric wiring H1 for supplying the pump cell current is not shielded similarly to the electric wiring H4 for the heater. May be changed so that the electric wiring H1 is also shielded.
[0069]
In the above-described embodiment, (1) the noise countermeasures for the electric wiring (such as a shield) and (2) the noise countermeasures (the installation of a feedthrough capacitor, etc.) for the case of the sensor control unit are both implemented. A configuration in which only one of (2) is implemented may be adopted.
[0070]
In addition to a gas concentration sensor (NOx sensor) capable of detecting a NOx concentration, the present invention can be applied to a gas concentration sensor (HC sensor, CO sensor) capable of detecting a HC concentration or a CO concentration as a gas concentration of a specific component. In this case, the pump cell (first cell) exhausts excess oxygen in the gas to be detected, and the sensor cell (second cell) decomposes HC and CO from the gas after exhausting excess oxygen to reduce the HC and CO concentrations. To detect.
[0071]
Furthermore, it is also possible to use it for a gas concentration detecting device other than those for automobiles, and to use a gas other than exhaust gas as a gas to be detected.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an outline of a gas concentration detection device according to an embodiment of the present invention.
FIG. 2 is a diagram showing a specific configuration of a sensor control unit.
FIG. 3 is a diagram showing a configuration of an electric wiring.
FIG. 4 is a diagram showing a configuration of an electric wiring.
FIG. 5 is a sectional view showing various forms of a shield coating.
FIG. 6 is a cross-sectional view illustrating a configuration of a gas concentration sensor.
FIG. 7 is an external view of a gas concentration sensor.
FIG. 8 is a diagram used for describing volume resistivity.
FIG. 9 is a diagram used for describing volume resistivity.
FIG. 10 is a diagram showing a configuration in which a shield is applied to a connector portion.
FIG. 11 is a diagram showing a specific configuration of a sensor control unit.
[Explanation of symbols]
10 ... Sensor control unit,
11 ... Sensor control unit,
12 ... heater control unit
30 ... case,
31 ... case body,
32 ... partition plate,
33 ... Sensor control circuit board
34 Wiring connection board
35 ... feedthrough capacitor,
41 ... core wire,
42 ... Coating layer,
43 ... Shield layer,
44… vinyl sheath,
51 ... circuit board,
52 ... partition plate,
60 ... connector part,
61 ... casing,
100: gas concentration sensor,
105 ... Sensor element,
110 ... pump cell,
120 ... monitor cell,
130 ... sensor cell,
141, 142 ... solid electrolyte,
151 ... heater,
H1 to H5: electric wiring.

Claims (17)

The present invention is applied to a gas concentration sensor including a sensor element having a solid electrolyte and detecting a gas concentration of a specific component in a gas to be detected and a heater for heating the sensor element to a predetermined active state. In a gas concentration detection device, a sensor control unit for measuring a weak element current flowing through the sensor element and intermittently energizing the heater is electrically connected to the gas concentration sensor through a wiring unit.
The wiring unit is formed by bundling an element current line for flowing an element current and a heater line for supplying power to a heater, and forming a shield layer having a ground potential outside the core wire through which the element current flows in the element current line. A gas concentration detection device comprising: 2. The gas concentration detection device according to claim 1, wherein, in the element current line, a periphery of the core wire is covered with a covering layer, and an outside of the covering layer is covered with the shield layer. 3. The gas concentration detection device according to claim 2, wherein the coating layer has a volume resistivity of 1.0 × 10 ¹² (Ω · cm) or more. The gas concentration detection device according to claim 2, wherein Teflon (registered trademark) is used as the coating layer. 5. The gas concentration detecting device according to claim 1, wherein the element current line has a plurality of core wires, and the plurality of core wires are collectively covered with the shield layer. The gas concentration according to any one of claims 1 to 4, wherein the element current wire has a core wire covered with a coating layer, a shield layer is provided outside the core wire, and a protection layer is further provided outside the core wire. Detection device. 5. The element current line according to claim 1, wherein each of the element current lines has a plurality of core wires covered with a coating layer, a shield layer is provided outside the plurality of core wires, and a protection layer is further provided outside the shield layer. The gas concentration detecting device according to any one of the above. 8. The gas concentration detecting device according to claim 1, wherein a ground process for connecting a shield layer of the element current line to a ground potential and a ground process for connecting the heater to a ground potential are separately performed. 9. The gas concentration detecting device according to claim 1, wherein the wiring unit is connected to the sensor control unit via a connector member, and a shield is provided on an outer periphery of the connector member. 10. An element current connector for connecting the element current line to the sensor control unit and a heater connector for connecting the heater line to the sensor control unit are separately provided. A gas concentration detection device according to any one of the above. The control circuit unit included in the sensor control unit is housed in a closed space of a case made of a conductive material and having a ground potential, a feedthrough capacitor is arranged on a wall of the case, and further electrically connected to the wiring unit. The gas concentration detection device according to claim 1, wherein a connection circuit portion is disposed outside the closed space, and the connection circuit portion and the control circuit portion are electrically connected to each other through a through capacitor. A case made of a conductive material and set to the ground potential is divided into two rooms by a partition plate made of the same conductive material and set to the ground potential, and a feedthrough capacitor is arranged on the partition plate and included in the sensor control unit. The gas according to any one of claims 1 to 10, wherein a control circuit unit and a connection circuit unit electrically connected to the wiring unit are housed in the two rooms, respectively, and the circuit units are electrically connected through a through capacitor. Concentration detection device. The present invention is applied to a gas concentration sensor including a sensor element having a solid electrolyte and detecting a gas concentration of a specific component in a gas to be detected and a heater for heating the sensor element to a predetermined active state. In a gas concentration detection device, a sensor control unit for measuring a weak element current flowing through the sensor element and intermittently energizing the heater is electrically connected to the gas concentration sensor through a wiring unit.
The control circuit unit included in the sensor control unit is housed in a closed space of a case made of a conductive material and having a ground potential, a feedthrough capacitor is arranged on a wall of the case, and further electrically connected to the wiring unit. A gas concentration detection device, wherein a connection circuit portion is disposed outside the closed space, and the connection circuit portion and the control circuit portion are electrically connected through a through capacitor. The present invention is applied to a gas concentration sensor including a sensor element having a solid electrolyte and detecting a gas concentration of a specific component in a gas to be detected and a heater for heating the sensor element to a predetermined active state. In a gas concentration detection device, a sensor control unit for measuring a weak element current flowing through the sensor element and intermittently energizing the heater is electrically connected to the gas concentration sensor through a wiring unit.
A case made of a conductive material and set to the ground potential is divided into two rooms by a partition plate made of the same conductive material and set to the ground potential, and a feedthrough capacitor is arranged on the partition plate and included in the sensor control unit. A gas concentration detecting device, wherein a control circuit section and a connection circuit section electrically connected to the wiring unit are accommodated in the two rooms, respectively, and these circuit sections are electrically connected through a through capacitor. 15. The gas concentration detection device according to claim 12, wherein the control circuit portion and the connection circuit portion are provided on the same circuit board, and the partition plate is provided between the two circuit portions so as to stand on the circuit board. apparatus. 16. The gas concentration detection device according to claim 11, wherein the capacitance of the feedthrough capacitor is 1000 pF or more. The sensor element includes a first cell that discharges or pumps oxygen in the gas to be detected introduced into the chamber, and oxygen ions that take in the gas after passing through the first cell, decompose a specific component in the gas, and move at that time. 17. The gas according to claim 1, further comprising a second cell for detecting a gas concentration of a specific component from the amount, wherein the sensor control unit measures at least a weak current flowing through the second cell. Concentration detection device.

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